These studies will define the binding sites of regulatory proteins to the yeast cytochrome c genes, and identify regulatory proteins which bind specifically to these genes. The approaches to be used involve in vitro mutagenesis of the genes followed by transformation of yeast cells and selection for transformants having the mutant phenotype. In addition, a fused gene system involving the 5 feet sequence of the yeast CYCl (iso-l-cytochrome c) gene and the structural region of the E. coli galK (galactokinase) gene will be used to allow selection of oxygen constitutive mutants. The precise location of the mutations obtained will be determined by DNA sequencing. The regulatory proteins will be identified and purified by the isolation of chromatin-complexed CYCl plasmids from yeast cells. Those proteins bound specifically to the CYCl DNA, and differentially bound to CYCl DNA in cells grown under anaerobic and aerobic catabolite repressed and depressed conditions, will be characterized.